This invention generally relates to a process of manufacturing of a packaging contaier such as a carton or the like made of reinforced corrugated cardboard, and more particularly relates to a process of manufacturing of a packaging container made of reinforced corrugated cardboard which has an improved pressure resisting property.
A corrugated cardboard packaging container is widely used for various packaging applications because it is light in weight and is strong in mechanical strength. But, when commodities to be contained therein are heavy in weight and the corrugated cardboard packaging container containing the commodities, are piled one upon another, there has been such a danger that the pressure applied to the container is beyond a limit of the pressure resisting strength owned by the corrugated cardboard itself and consequently there takes place deformation or breakage of the packaging container. For this reason, as seen in Japanese Utility Model Laid-open Application No. 52-84427, it has been proposed that the pressure resisting strength of a packaging container is improved by applying of a reinforcing agent to the core of the corrugated cardboard forming the four side portions the body of the packaging container.
However, in a case of using of the container of which the side portions are reinforced, when such plural containers containing heavy commodities are piled one upon another scored line portions b thereof are crushed by pressure as shown in FIG. 6, and additionally flaps c thereof are caved in inside the side portions a as shown in FIG. 5, so that the interior dimensions of the container is decreased to such an extent that the container becomes unsuitable for reuse or is liable to be broken at the scored line portions b. In the above view, the invention of this application has previously proposed such a reinforced corrugated cardboard packaging container in Japanese Utility Model Application No. 53-12420 that reinforcement treatment is carried out not only on the scored line portions b of the flap, but also to extend to the sides a of the container as shown in FIGS. 1 and 2.
It has been confirmed that in manufacturing of the reinforced corrugated cardboard packaging container, if reinforced corrugated cardboard manufactured by a conventional reinforced corrugated cardboard manufacturing process is used, the object of the reinforcement cannot be fully attained. Namely, the conventional process of manufacturing of reinforced corrugated cardboard is such that a sheet of cardboard is previously applied with a reinforcing agent, and then is formed by pressing into a corrugated core liner and thereafter the front and back liners are adhered in order to both side surfaces thereof to obtain reinforced corrugated cardboard, and thereafter the reinforced corrugated cardboard is applied with a scoring step so that scored lines are formed in the cardboard, a packaging container is formed thereby.
When the scored lines are thus formed, since the reinforcing agent of the core liner has been earlier hardened through heating and drying by a preheater and through heating during corrugation forming, the portions of the corrugated cardboard reinforced with the reinforcing agent is crushed and its structure is destroyed on forming the scored lines therein by a scorer, so that when the portions are applied with pressure in piled condition of the containers, the same is bent as shown in FIG. 6, and the purpose of reinforcing of the scored lines is meaningless.